PRODUCTION  OF  GREEN  SURFACE  COLORS  ON  RED-BURNING 

SHALES 


By 


EARL  BOGGESS  BAKER 


THESIS 


FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CERAMIC  ENGINEERING 


COLLEGE  OF  ENGINEERING 
UNIVERSITY  OF  ILLINOIS 


\ 


V • 


,T/. 

Ij 


476973 


It 


■■i.rro^  ' iic 


Digitized  by  the  Internet  Archive 

in  2016 


https://archive.org/details/productionofgreeOObake 


TARLF.  OF  COFTEFTS 


P n p-  c 


I IITTROPUCTIOF 1 

II  EXFERIICENTAL  PROCEPITPE 3 

1.  General  plan 3 

2.  Materials  used 5 

III  E10PERIL31TTS  AllP  RESULTS 6 

IV  SCOPE  or  nrvES^IGATIOIT 9 

V SUIU’T/JIY  OF  results  9 

VI  GEITEK.AL  COUCIUSICFS 10 

VII  BIELIOGPAPKY 11 


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I 


INTRODUCTION 


The  demand  for  new  and  novel  color  and  texture  effects  on 
face  brick  has  induced  a great  development  in  mechanical  devices 
and  in  firing  treatments  for  the  production  of  such  effects.  Green 
colors  are  much  desired  by  many  producers  who  recognize  their 
possibilities  in  the  market.  These  colors  must  generally  be  com- 
bined v/ith  surface  textures  mechanically  produced.  Grazed  brick 
v;ill  scarcely  fulfill  the  requirements  owing  to  difficulties  in 
manufacture  and  in  firing,  such  ware  and  the  expense  of  producing 
it . 

In  som.e  instances  green  sha.des  appear  on  normally  red- 
burning  clays  in  certain  portions  of  a kiln  but  the  production  in 
quantity  has  not  been  attained  by  more  thon  a few  manufacturers. 
Obtaining  of  such  colors  apparently  depends  upon  the  firing  treat- 
ment as  well  as  the  composition  of  the  clay. 

Limited  information  is  available  from  ceramic  literature 
on  green  color  production,  other  than  in  glazes.  In  these,  the 
coloring  agent  ma,y  be  copper,  chromium  or  a ccjmbinat i on  of  uranium 
and  cobalt.  In  some  cases  iron  may  give  a green  coloration. 

This  may  be  especially  noted  in  glasses  containing  iron  as  an  im- 
purity. Calcium,  barium  or  magnesium  probably  aids,  but  iron 
unquestionably  functions  as  a coloring  agent  in  the  case  of  green 
surface  effects  on  clays. 

Seger ^ f requ ently  refers  to  calcium  as  an  aid  in  the  form- 
ation of  greens.  He  states,  ” Sy  the  reducing  action  of  fire  gases 
an  iron  bearing  clay  beccrnes  an  intense  uniforir.  black  due  to  uhe 


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fonnation  of  f erroso-f er  lic  oxide,  ferrous  oxide  and  metallic  rion. 

By  a previous  reduction,  an  oxidizing  atmosphere  produces  sha.des  of 
a lighter  color,  passing  into  white  or  light  green".  He  further 
states  that  in  either  oxidizing  or  reducing  atmospheres  sulphur  is 
ahsorhed  hy  calcium  and  iron  in  cal  care  ous|cl  ays  and  gives  a dense 
red  color  at  moderate  red  heat.  The  red  is  completely  destroyed 
at  a high  temperature  and  is  changed  to  the  normal  greenish  yellow 
color  by  the  action  of  reducing  gases. 

Lime  produces  a neutralizing  effect  on  iron  colorations. 

A yellow  burning  calcareous  clay,  when  the  chemically  combined  water 
has  been  expelled,  becomes  red  and  still  further  heating  changes 
it  through  white  into  yellov;  and  orange  until  finally  on  vitrifica- 

R * 

tion  the  color  becomes  green. 

In  a strongly  reducing  atmosphere,  a glaze  containing  2 % 

of  iron  oxide  and  10  % calcium  gives  a greenish  blue  similar  to  the 

color  of  Chinese  Celadon  or  " sea  green".  Such  greens  are  complete- 

4 

ly  destroyed  in  an  atmosphere  containing  20^^  of  carbon  monoxide. 

I’roin  the  literature,  a most  logical  treatment  for  the 
production  of  green  surface  colors  or  normally  red-burning  shales 
would  seem  to  be  the  addition  of  varying  percentages  of  lime, 
magnesium  or  possibly  barium  and  firing 
and  reducing  conditions. 


under  varying  oxidizing 


J ' . . 


-3- 


II  EXP]!UlIT,tENT./\L  PROCEDURE 

1.  General  plan.-  The  general  plan  of  procedure  in 
the  experiments  consisted  in  firing  prepared  trial  pieces  to  tempera- 
tures ranging  from  950®  to  1150®C,  and  under  varying  atmospheric 
conditions.  These  treatments  produced  "bodies  varying  from  a porous 
structure  to  those  of  a complete  vitrification. 

The  atmospheric  conditions  were  varied  from  slight 
reductions  followed  "by  either  long  or  short  oxidizing  periods  to  that 
of  heavy  reduction  followed  by  either  short  or  long  oxidizing  periods 
for  the  respective  heat  treatments.  Similar  reduction  and  oxidation 
treatments  were  repeated  v/ith  a period  of  neutral  atmosphere 
follov;ing  each  reduction. 

The  experiments  were  carried  out  partly  in  a coal  fired 
test  kiln  and  partly  in  an  electrically  heated  combustion  furnace. 

In  the  coal  fired  kiln  reducing  and  oxidizing  conditions  were 
maintained  in  the  usual  manner  by  damper  and  fire  control.  Atmos- 
pheric conditions  in  the  electric  combustion  furnace  v;ere  regulated 
by  use  of  city  gas  or  carbon  monoxide  for  reduction  and  carbon 
dioxide  for  neutral  and  air  for  o-idizing  conditions. 

The  electric  furnace  and  supplementary  apparatus  is 
shown  in  Eig . ITo.  1.  Carbon  dixoide  was  produced  by  means  of  the 
Kipp  generator  c attaining  chips  of  marble  and  dilute  hydrochloric 
acid.  Carbon  monoxide  was  produced  by  passing  the  carbon  dioxide 
over  charcoal  heated  in  an  electric  combustion  furnace.  Eor  an 
approximate  control  of  gas  mixtures  entering  the  furnace,  all  gases 
v/ere  bubbled  through  water.  An  Orsat  apparatus  v;as  used  for 


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-5- 


deterrnining  the  cmposition  of  gases  entering  the  furnace. 

2.  Materials  used.~  'i’rial  pieces  were  prepared  of 
sliales  obtained  from  Galesburg,  Illinois;  Alton,  Illinois;  and 
ij’ort  Dodge,  Iov;a.  With  the  exception  of  a small  amount  of  limey 
over-burden  accompanying  the  I’ort  Dodge  shale,  all  lime,  magnesium 
and  barium  was  added  in  the  form  of  the  carbonates. 

The  follov/ing  mixtures  were  prepared: 


Mixture 

No 

. 1 

Alton  shale 

100% 

n 

II 

2 

- 

Galesburg  s 

hal e . . . 

.1 

II 

3 

- 

Fort  Dodp;e  limey  over-burden.  - . . 100 

II 

It 

,A_ 

Fort  Dodge 

shale . . 

100 

n 

ft 

5 

Fort  Dodge 

shale  - 

-75%.  . .li 

,mey  over- 

burden .25 . 9 

H 

tl 

6 

• 

II  II 

II 

87.5 

II  II 

12.5 

tl 

tl 

7 

.. 

II  II 

II 

99.9 

BaC  0, 

II 

0.10 

II 

II 

3 

11  n 

If 

99.35 

0.15 

II 

11 

9 

II  II 

tt 

99.30 

11 

0.20 

U 

ft 

10 

II  II 

ft 

93.00 

CaCo., 

2.00 

II 

II 

11 

- 

II  II 

II 

96.00 

II 

4.00 

f1 

It 

12 

- 

II  It 

II 

94.00 

If 

6.00 

II 

II 

13 

- 

II  n 

n 

90.00 

II 

10.00 

II 

II 

14 

11  ?f 

n 

35.00 

II 

15.00 

1! 

II 

15 

* 

tl  II 

II 

93.00 

MgCo„ 

2.00 

II 

II 

16 

- 

It  II 

n 

96.00 

II  o 

4.00 

11 

n 

17 

11  II 

H 

94.00 

n 

6.00 

II 

II 

18 

II  If 

II 

90.00 

II 

10.00 

tl 

!? 

19 

II  II 

n 

35.00 

II 

15.00 

II 

II 

20 

Galesburg  shale 

93-00 

CaCo 

2.00 

II 

II 

21 

II  It 

tt 

96.00 

II  3 

4.00 

II 

If 

no 

* 

II  T) 

II 

94.00 

II 

6.00 

II 

II 

23 

ft  II 

i! 

90.00 

II 

10.00 

II 

II 

24 

IS  It 

If 

85.00 

II 

, 15.00 

II 

II 

25 

- 

No. Carolina 

kaolin 

55.00  grs. 

SiO,. . .. 

35.00  ” 

Fe^ot . . . . 

O • 

2 3 

CaO 

10.00  ” 

K 0 

25.00  *' 

i4o 

lO 
1 — 1 

It 

ft 

26 

- 

Galesburg  sh 

.£j.e  (lOO,"^)  dipped  in  CaS  O^g  olut ion . 

Mixture  No. 

25 

was 

determined  by 

calculating  the 

average 

composition 

of  Celadon  glaze. 


1 


-6- 


III  EXI^ERIKENTS  jMTD  KSSUiyrS. 


The  first  nineteen  of  the  series  of  mixtures  v;ere 
fired  in  a coal  kiln.  This  was  in  the  nature  of  a preliminary  sur- 
vey f r on  which  more  definite  pl^ns  could  he  determined.  trials 
were  drawn  at  intervals  of  ?5°C  between  950°  a.nd  1150°C,  eacn  after 
a reduction  period  of  fifteen  minutes  follov;ed  hy  an  oxidizing 
period  of  45  minutes.  The  temperature  was  held  constant  for  each 
trial . 


Below  the  vitrifying  temperature  of  the  various  trials, 
the  colors  ranged  from  deep  red  to  light  gray  with  variation  frcra 
low  to  hi^'h  CaCO  , MgCO  and  BaCO  content.  As  the  trials  become 

"333 

vitrified,  their  colors  ranged  from  black  to  dark  brovm  v;ith 

variation  from  low  to  high  content  of  CaCO^,  MgCO^  and  BaCO^. 

This  treatment  represents  commercial  limits  both  as  to  ternperatuie 

treatment  and  additions  of  ^aCO  , MgCO  and  BaCO  . Clays  contain- 

33  3 

ing  more  then  15  ^ of  the  respective  carbonates  are  limited  in 
commercial  use  due  to  the  cost  of  the  carbonates  and  to  tne  increase< 
heat  treatment  to  produce  me.turity.  Eroin  this  test  it  was 
learned  that  perma.nent  surface  colors  can  not  be  produced  by 
atmospheric  conditions  before  the  body  has  become  vitrified. 

The  remaining  mixtures  were  given  a preliminary  heat 
treatment  in  a gas  kiln  in  order  to  expel  all  carbonaceous  material 
before  firing  thera  in  the  electric  furnace.  Of  the  mixtures  con- 
taining CaCO  , only  those  containing  less  than  10^^  could  be  tested 
3 

due  to  the  increased  refractoriness  with  higher  lime  content 
and  the  limited  temperature  range 


of  the  furnace. 


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4 % of  ^aCO  , was  subjected  to  varj^ing  heat  treatments  giving  a body 
3 

ranging  from  _orous  to  completely  vitrified.  For  the  different 
heat  treatments,  the  atmospheric  conditions  in  the  furnace  were 
varied  fran  strong  reduction  by  means  of  city  ga,s , followed  by  long 
oxidation  periods  to  light  reductions  followed  "by  short  oxidation 
periods.  Such  treatments  resulted  in  color  effects  similar  to 
those  produced  in  the  coal  kiln.  -Below  vitrification,  the  pieces 
were  of  a light  red  color  but  upon  becoming  vitrified  the 
reduction  resulted  in  permanent  colors  varying  from  dork  brovm 
to  black,  the  colors  becoming  darker  with  more  intense  reduction. 

'i’he  dark  coloration  was  chiefly  due  to  a reduction  in  the  iron  in  the 
clay  to  ferrous  or  metallic  iron  and  the  density  of  the  vitrified 
body  prevented  a re- oxidation.  From  these  results  it  was  again 
evident  that  a permanent  green  color  could  not  be  produced  on  a non- 
vitreous  body. 

It  was  next  thought  advisable  to  follow  each  reduction  by 
a period  in  a neutral  atmosphere  before  introducing  oxidizing  con- 
ditions. To  obtain  the  neutral  atmosphere,  carbon  dioxide  from  a 
hipp  generator  v;as  passed  through  the  furnace.  -^'rom  the  assumption 
that  a green  coloration  is  a result  of  the  formation  of  an  iron- 
lime-silicate,  it  v/as  hoped  that  a period  under  neutral  atmospheric 
conditions  would  give  additional  time  for  such  a chemica.1  reaction 
to  become  more  complete  before  introducing  an  oxidizing  atmosphere. 
The  use  of  a neutral  atmosphere  gave  the  same  results  as  y/ere 
obtained  v/hen  the  reduction  was  followed  immedia,tely  by  the  oxidation 
period. 


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The  next  treatment  consisted  of  vitrifyin.:-  the  trial 
and  then  subjecting  it  to  several  moderate  reduction  periods,  each 
followed  by  a cooling  of  the  piece  in  an  oxidizing  atmosphere. 

The  latter  was  accomplished  by  withdrav/ing  the  trial  fron  the  fur- 
nace for  a short  time  after  which  it  was  again  placed  in  the  furnace 
and  given  a similcr  treatment.  ''.Vith  two  such  treatments  a 
distinct  bluish  green  color  was  obtained  which  did  not  change  with 

repetition  of  the  treatment.  A small  piece  of  mixture  No.  21 

\ 

was  dipped  in  water  previously  saturated  with  calcium  sulfate. 

After  drying  the  piece  was  placed  in  the  furnace  and  heated  to 
vitrification.  Upon  vitrifying  the  trial  overburned  and  sv/elled 
thus  eliminating  it  frotn  practical  conside  rati  on . Calcium  sulfate 

will  deccmpose  to  a greater  or  less  extent  v/hen  hea.ted  in  the 
presence  of  iron  and  silica.  5’rom  this  fact  it  v/as  thought 
possible  to  decompose  the  sulfate  thus  leaving  the  calciujn  in  the 
body  to  combine  with  the  iron  and  silica..  This  result  might  have 
been  obtained  by^  further  testing  but  it  v/ould  be  of  no  practical 
value  since  portions  of  kilns  are  often  overfired  and  this  v/ould 
produce  a tilting  of  the  vrare. 

Reducing  conditions  were  finally  produced  by  passing 
carbon  dioxide  over  hot  charcoal  in  a combustion  furnace.  By 
varying  the  temperature  fran  650®C  to  700°C,  the  carbon  monoxide 
content  of  the  gas  varied  from  8 to  20  %• 

Mixture  No.  21  was  given  reduction  treatments  with  gases 
containing  8%  and  a.gain  v/ith  gases  containing  20^  carbon  monoxide. 
Both  resulted  in  a dark  blue  coloration.  Further  investigation 


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-9- 


mi£;ht  have  given  more  satisfactory  results  v/ith  the  use  of  carbon 
monoxide  as  the  reducing  agent. 

Mixture  No.  25,  consisting  of  North  Carolina  kaolin  55 
silica  dixoide  35,  ferric  iron  3.5,  calcium  oxide  10,  potassium  oxide 
5,  and  magnesium  oxide  1.5,  was  vitrified  and  reduced  by  means  of 
city  gas.  By  a single  cooling  in  the  air  a good  green  color  was 
ootained.  The  chief  difficulty  was  due  to  a very  short  vitrifica- 
tion range  which  resulted  in  giving  the  piece  a marked  glaze  effect. 
This  v;as  undoubtedly  a result  of  the  fluxing  action  produced  by  the 
chr-mge  of  ferric  to  ferrous  iron  and  the  high  lime  content.  Trials 
drawn  belov;  the  vitrification  point  v/ere  of  a.  reddish  brov.Ti  color. 

IV  SCOPE  OP  lilVESTIGATION 

The  scope  of  this  investigation  was  limited  practically 

to  a study  of  the  temperature  and  atmospheric  conditions  favoring 

the  development  of  a green  surface  coating.  A study  of  the  body 

compositions  v/as  iripossible  until  a.  proper  firing  treatment  was 

a 

obtained  after  which  only^linited  amount  of  tiine  remained  for  further 
inves  tigati on . 

V SmMARY  OP  RESULTS 

The  results  of  the  above  invest igati ons  may  be  siAirmar- 
ized  as  follov;s. 


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-10- 


1 .ColorstioriR  produced  on  a.  porous  ferruginous  cla.y 
"body  liy  means  of  reducing  conditions  in  firing  were  not  permanent. 

2. Wlien  vitrified,  a ferruginous  cl-y  v;ill  retain  sur- 
face colors  imparted  to  it  "by  reducing  action  of  kiln  gases. 

3.  A red.ucti.  on  "^eriod  fallowed  "by  an  oxidation  period 
at  the  same  temperature  did.  not  give  a green  surface  color. 

4.  A reduction  period  followed  by  an  oxidation  period 
accompanied  by  a cooling  of  the  cloy  is  favorable  for  the 
production  of  a green  surface  color. 

5.  The  presence  of  lime  in  ferruginous  shale  is 
favorable  for  the  production  of  green  surface  colors  when  given  the 
proper  firing  treatment. 

6.  A neutral  jjeriod  following  each  reduction  is  un- 
to  aid  in  better  surface  colors. 


V I GMIEH AI.  C '"FGT  ng  t OITG 


Fr  cm  the  ab  o ve  r e su Its, 


the  following  conclusions  ma.y  be 


drawn: 


1.  A red-burning  shale  containing  4 to  6%  of  ca.lcium 
carbonate  will  give  a green  surface  color  if  fired  under  favorable 
conditi ons . 


2.  5'avorable  atmospheric  conditions  for  the 
production  of  green  surface  colors  consist  of  moderate  reductions 
followed  by  strong  oxidizing  periods  accompanied  by  cooling. 

3.  The  heat  treatment  of  any  "ware  for  tine  production 
of  0.  surface  color  must  be  sufficient  to  produce  complete  ■vi^ro.j.i- 


ca  t i on . 


] 

f 


• 

i, 

Jv’ 


*1 


/ 


-11- 


4.  The  £;rcen  coloration  ic  prohahly  due  to  the 
fonnation  of  an  iron-lime-silicate. 

VII  BIBLIOGRAPHY 

1.  The  Hole  playet?  hy  iron  in  the  burning  of  clays  - 
Professor  i^^dward  Orton.  Trans.  Amer.Ceraia.  Soc.  Vcl.5,  p.  377 

2.  The  compositjon  of  Chinese  Celadon  pottery.  - 

Jour.  Amer.  Cerain.  Soc.  Vol.  2 - p.  55. 

5.  Influence  of  oxidising  and  reducing  geses  on  the 
color  imparted,  to  porcelain  by  coba.lt  and  iron.  Professor  E. 
Bemiour.  Jour.  Soc.  of  Chemical  Industry’.  Vol.15,  p.  533 

4.  Porcelain,  influence  of  the  a,tmosphere  of  the  kiln 
on  colors.  Professor  E-Bemour.  Jour.  Soc.  of  Chemical  Industry. 
Vol.  17,  p.  S45. 

5.  Calcium  carbona.te  in  clay  and  its  influence  on  the 
properties  of  the  latter,  y^-ith  special  regard  to  the  manufacture 
cf  front  brick.  Seger,  Vol.  1 - p.  336. 

6.  The  comiposition  of  Augite.  Professor  Edv/ard  S.Bana. 
A System  of  Mineralogy  - p.  481. 

7.  Mote  on  brick  colors.  Professor  -German  A.Seger  - 
The  Collection  of  Writings  of  Herman  A.Seger.  Vol.l,  p.  106. 


